One common use of instrumentation in a manufacturing environment is to determine rapidly “figures of merit” of a manufactured electronic component or system. Such figures of merit are used both to determine the quality of component or system, and also to enable the component or system to be optimized relative to its performance specification.
For example, in the manufacture of amplifiers for wireless base stations, nonlinear figures of merit such as third-order intercept are typically used in the tuning process, and figures of merit such as the adjacent channel power ratio are used to check final compliance of an amplifier with federally mandated specifications. In the design of an entire wireless base station on the other hand, the error-vector-magnitude is monitored across different sub-components of the base station in an attempt to optimize the overall bit error rate (BER) or correlation coefficient (ρ) of the transmitter. Thus, various figures of merit come into play in developing and manufacturing a component or system, and how they are used depends on a mix of issues both practical and legal.
Typical figures of merit that play a key role in the manufacturing and testing of radio frequency (RF) and microwave components and systems are so-called:                Correlation Coefficient (ρ),        Error Vector Magnitude (EVM),        Adjacent Channel Power Ratio (ACPR), and        Third-Order Intermodulation Distortion (IMD).        
The first two of the above figures of merit, ρ and EVM, defined in terms of time domain signals (see for example Testing and Troubleshooting Digital RF Communication Receiver Designs, Agilent Application Note AN 1314, pp. 1-24, Mar. 25, 2002), attempt to summarize the distortion produced by a system in terms of an average difference in the time domain between the specified and observed behavior of a stimulus and response signal. The latter two figures of merit, ACPR (see for example Understanding CDMA Measurements for Base Stations and Their Components, Agilent Application Note AN 1311, pp. 1-36, June 2000) and IMD (see for example Third Order Intermodulation Distortion Measurements, Agilent Product Note PN 8566B/8568B-1, 5954-2701, pp. 1-6, October 2000), are defined in the frequency domain, and are quantities which can be computed from a power spectral density (PSD) function using a fast Fourier transform (FFT). However, all four figures of merit are estimated in prior art instrumentation through a stimulus and response measurement on each device under test (DUT), which uses no prior information about the DUT. Moreover, each figure of merit is computed by an independent stimulus and response measurement, even on the same DUT. The advantage of this prior art approach is that the instrument is able to provide information about a large range of different types of devices or systems, since the algorithms used to compute the relevant figure of merit do not depend on the type of DUT. A drawback, however, is that a great deal of data and thus of measurement time is required to accurately estimate a single figure of merit for a single DUT.